Metal rendering shows incorrect color, gputrace shows fragment function returning correct color

I'm experiencing a strange issue where I'm seeing black in a metal drawable where it should be a different color. When I capture the frame and inspect the returned value from the fragment function, it's correct, but the drawable isn't.

This screenshot hopefully illustrates the issue.

I've not found any references to similar issues. I saw something about some out of bounds or NaN values being dropped to 0 (which would be black), but the debugger doesn't indicate this is happening.

Another example from a unit test, where the color isn't black but is definitely not what the fragment shader is returning.

Metal rendering shows incorrect color, gputrace shows fragment function returning correct color
 
 
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